There has been known a 7 segment display unit as a conventional display unit for displaying an alphanumeric character. The 7 segment display unit can display numeric characters, 0 to 9 and only 8 alphabetic characters, A, C, F, E, U, P, H and L (in capital letters).
In order to eliminate this inconvenience, there has been provided a dot matrix display unit comprising a 5×7 dot display. However, 35 display elements are required to construct the dot matrix display unit and furthermore, the dot matrix display unit can display an alphanumeric character in only a circular pattern or a square pattern.
There has also been conventionally known an alphanumeric display type display unit as a display unit for displaying an alphanumeric character. This display unit, however, has difficulty in displaying an alphabetic character correctly and is inferior to the other conventional display units in visibility, so that it does not become widely used.
For example, JP-A No. 2000-47603 discloses a display unit capable of displaying more of information and being manufactured at lower cost. The display unit described in JP-A No. 2000-47603 comprises plural segment electrodes corresponding to plural display segments, and a common electrode disposed oppositely to the segment electrodes with a TN type liquid crystal interposed therebetween. One display digit for presenting an alphanumeric character and the others is constituted of the segment electrodes and the common electrode arranged oppositely to the segment electrodes.
In this display unit, the segment electrodes are divided into 4 groups and 4 common electrodes are assigned to the respective 4 groups. According to this construction, the amount of common driving signals and segment driving signals and the number of wiring patterns are greatly reduced, so that manufacture of the display unit is achieved at low cost with increase in the amount of information that can be displayed on the display unit.
The display unit described in JP-A No. 2000-47603 basically corresponds to an improvement on the conventional 7 segment display unit. In this display unit, two 7 display segment digits (display digits) are arranged in two lines in a lateral direction, one oblique display segment is provided between the digits or in a portion surrounded with the 7 display segments, or alternatively, four small display segments are arranged in the shape of an alphabetic character “x” to increase an amount of information that can be displayed. According to this basic configuration, a katakana character of voiceless sound and a special symbol can be displayed together with an alphanumeric character, and furthermore, a katakana letter of voiced sound or a p-sound can also be displayed by providing more of display digits additionally.
According to the display unit described in JP-A No. 2000-47603, however, even though it is provided with the basic construction for displaying an alphanumeric character (including a katakana character of voiceless sound and a special symbol), not only are 29 display segments required, but at least five kinds of display segments of different shape and size are also required. Hence, a manufacturing cost of a display segment itself increases and besides, the display segments have to be arranged in a specific complex pattern, which makes lighting-on and -off control of wiring and display segments complicated. In a case where the display segments are formed with light emitting diodes, brightness of the light emitting diode elements are fluctuated when the display segments are of different shape and size.